Method of making flexible loop, hard slot coils for dynamoelectric machine windings

ABSTRACT

A flexible loop, hard slot coil is described wherein the preformed coil is wrapped over the entire coil length with a single micaceous insulating tape. The resin system applied between tape layers wrapped about the slot regions of the coil, however, contains a greater weight percentage of cross-linking catalyst than is contained in the resin system applied atop the loop regions of the coil to produce a differential cure rate for the different sections of the coil, i.e., the resin system in the slot sections of the coil becomes fully cured during subsequent baking of the coil while the resin system in the loop portions of the coil remains partially cured to retain flexibility therein. Flexible loop, hard slot coils also can be fabricated by varying the weight percentages of epoxide resins forming a resin blend to produce a more rapid cure rate in the slot portions of the coil relative to the loop portions of the coil. The resultant flexible loop, hard slot coil not only facilitates winding of dynamoelectric machines by permitting &#39;&#39;&#39;&#39;raising of the jump&#39;&#39;&#39;&#39; in a cold state but also eliminates the need for a high degree of precision in the drop angle of the coil loops.

3,750,273 Aug. 7, 1973 METHOD OF MAKING FLEXIBLE LOOP,

HARD SLOT COILS FOR DYNAMOELECTRIC MACHINE WINDINGS lnventor:

[75] Norman Anthony Beddows, Scotia,

General Electric Company, Schenectady, N.Y.

Filed: Nov. 18, 1971 Appl. No.: 199,845

Assignee:

[56] References Cited UNITED STATES PATENTS 7/1956 Botts et al 310/20812/1971 Kimura et al. 156/56 2/1963 Kitson, Jr. et al. 310/208 7/1969Mertens 156/330 5/1972 Anderson 310/208 Primary Examiner-Charles W.Lanham Assistant Examiner-Carl E. Hall AttorneyVale P. Myles et al.

[57] ABSTRACT A flexible loop, hard slot coil is described wherein thepre-formed coil is wrapped over the entire coil length with a singlemicaceous insulating tape. The resin system applied between tape layerswrapped about the slot regions of the coil, however, contains a greaterweight percentage of cross-linking catalyst than is contained in theresin system applied atop the loop regions of the coil to produce adifferential cure rate for the different sections of the coil, i.e., theresin system in the slot sections of the coil becomes fully cured duringsubsequent baking of the coil while the resin system in the loopportions of the coil remains partially cured to retain flexibilitytherein. Flexible loop, hard slot coils also can be fabricated byvarying the weight percentages of epoxide resins forming a resin blendto produce a more rapid cure rate in the slot portions of the coilrelative to the loop portions of the coil. The resultant flexible loop,hard slot coil not only facilitates winding of dynamoelectric machinesby permitting raising of the jump in a cold state but also eliminatesthe need for a high degree of precision in the drop angle of the coilloops.

5 Claims, 5 Drawing Figures h z'nd :onduclor: and share info 60:!aonfifqarafz'on,

h mzv coil will: mz'caceoas 6190' Neal zhs'alaiiny ape and.s'z'nza/fdneous'l [was/z d ,f d s'z' carz'ny resin info Zize 5/0!rqqzbns 0/ [be coil and a i/owzr an? resin, z'zr fie hop regions Irecoi/ PAIENTEDAUG H915 3,750,273 r SHEEI 2 [IF 4 METHOD OF MAKINGFLEXIBLE LOOP, HARD SLOT COILS FOR DYNAMOELECTRIC MACHINE WINDINGS Thisinvention relates to pre-formed coils for dynamoelectric machines and toa method of fabricating machines utilizing the pre-formed coils. Moreparticularly, the invention relates to a flexible loop, hard slotpre-formed coil having a resin system throughout the coil with differingcure rates in the slot and loop portions of the coil to facilitateinsertion of the coils into a magnetizable machine member.

In winding dynamoelectric machines with pre formed coils, i.e., closedloop coils shaped into a desired configuration and insulated beforeinsertion into the machine slots, it generally is necessary to liftpreviously inserted coil sides from machine slots to permit the sides ofsubsequently wound coils to be positioned therebelow. When thepre-formed coil is coated with a rigid insulation system, such as thecommonly utilized epoxy resin insulation systems, raising of the coilside places mechanical stress on the coil insulation tending to producecracks therein. One technique customarily employed to facilitate raisingof coil sides from the slots is to heat the loops, or end turns, of thecoil above the glass transition temperature of the insulating resin tosoften the resin sufficiently to inhibit cracking due to physicaldistortion of the loops. While heat treatment of the loops facilitatesraising of the coil sides, such treatment significantly increases thetime required to wind a machine and can be deleterious to the coilinsulation if the insulation undergoes a rapid heat rise in treatment.

An alternative method employed to facilitate winding of machines bycompletely eliminating the necessity for raising previously insertedcoil sides is described in I-I.D. Snivelys U. S. Pat. No. 3,631,278which issued Dec. 28, 1971 and assigned to the assignee of the instantapplication. This method, as described in the patent, generallycomprises the utilization of pre-formed coils offset in differentdirections to wind deep slot machines, i.e., machines having a group ofslots having a depth at least one coil side deeper than the coil sidesto be inserted therein. While dual offset coils are extremelyadvantageous in facilitating the winding of machines wherein excess slotdepth is required for cooling purposes, such coils generally are notsuitable in machines wherein the slot depth is substantially equal tothe total depth of the conductor sides to be inserted therein.

It also has been suggested that pre-formed coils be wrapped with a resinimpregnated micaceous tape along the slot sections of the coil and theloops be wrapped with a porous tape having a resin liquid brushedbetween successive layers of the tape to produce a hard ,slot, flexibleloop coil for facilitating the raising of coil sides. Coil windingutilizing different tapes, however, requires scarfing, i.e., theextremely time consuming process of inter-winding nonhomogeneous tapes,at the juncture of the tapes along the coil.

It is therefore an object of this invention to provide a flexible loop,hard slot coil which can be easily manufactured at reduced cost.

It is also an object of this invention to provide a coil having diverseflexibility characteristics along the coil length without need to scarfthe taping applied to the coil.

It is a further object of this invention to provide a flexible loop,hard slot coil having a gradual transition in rigidity from the loop tothe slot regions of the coil.

It is a still further object of this invention to provide. a coilwherein extremcaccuracy is not required in the geometric configurationof the coil.

It is a still further object of this invention to provide a method ofmanufacturing a dynamoelectric machine utilizing pre-formcd coils havingfully cured slot sections and partially cured loop sections tofacilitate raising of the jump during machine winding and repair.

These and other objects of this invention generally are achieved by apre-formed coil characterized by a plurality of conductors wound in aclosed loop and shaped to a coil configuration characterized byelongated slot regions for insertion in axially extending cavities of amagnetic member of a dynamoelectric machine and loop regionsinterconnecting the ends of the slot regions. The entire length of thecoil is wrapped with a homogeneous tape having a thermosettinginsulating system impregnated therein. The portion of the insulatingsystem impregnated within the tape wrapped atop the slot regions of thecoil, however, is completely cured to a rigid mass while the portion ofthe insulating system impregnated within the tape wrapped atop the loopregions of the coil is only partially cured, i.e., cured to a non-tackystate, to provide a flexible loop, hard slot coil. Preferably, thedifferential cure in the coil is achieved by the differential additionof a crosslinking promoter to the resin impregnated within the tapewrapped about the coil although a differential degree of rigidity alsocan be achieved by changing the weight percentage of epoxy resins'alongthe length of the coil when the thermosetting insulating resin systememployed for the coil is a blend of a suitable promoter and two or moreepoxide resins having different degrees of functionality andcomposition.

Although this invention is described with particularity in theappendedclaims, a more complete understanding of the invention may beobtained from the following detailed description of various specificembodiments taken in conjunction with the appended drawings wherein:

FIG. 1 is a flow chart illustrating in block diagram form a method offorming a flexible loop, hard slot coil in accordance with thisinvention,

FIG. 2 is an isometric view of a coil formed in accordance with thisinvention,

FIG. 3 is a sectional view of a hard slot, flexible loop coil duringprocessing,

FIG. 4 is a partial view of a dynamoelectric machine wound with theflexible loop, hard slot coils of this invention, and

FIG. 5 is a flow chart illustrating in block diagram form a method offorming a flexible loop, bard slot coil having superior insulatingcharacteristics.

Referring more particularly to FIGS. l-3, a flexible loop, hard slotcoil 10 in accordance with this invention is formed by initially windinga plurality of resin coated rectangular copper strands 12 into a closedloop whereafter the loop is shaped into a coil configuration utilizing acommercially available coil pulling machine. The entire coil then iswrapped with a porous micaceous tape 14 utilizing any conventional laparrangement, typically one-half lap although other commonly utilizedtaping arrangements such as three-fourths lap can be employed whenincreased resistance to damage by the transmittal of stress is desired.During lapping of the tape 14 atop coil 10, a single insulating resinsystem, such as a blend of Union Carbides ERL 4221 and Emery IndustriesInc. Dimer acid 1014 (an acid produced by the dimerization of C18unsaturated fatty acids) in weight ratios of 0.8:1, 1:1, and 111.2, isapplied between successive laps of the micaeeous tape. In order toobtain a differential cure rate in slot region 16 relative to loop, orend turn, region 18 of the coil, a small quantity of a cross-linkingpromoter is added to the resin applied between laps of the tape wrappedabout the slot region of the coil. For example, when the blend of ERL4221 and 1014 in a 1:1 ratio is used as the insulating resin system, 1percent by weight of tin- (ll)oetoate typically would be added to theresin applied to the slot region of the coil to produce an acceleratedcure of the slot region. After coil 10 is subsequently baked, e.g., at150C for hours, to cure the insulation system, the slot regions of thecoil are rigid and the loop regions are flexible. This facilitatesraising the jump in a cold state. Prior to baking, coil is characterizedby a liquid resin coated tape wound about the entire length of the coilwith the liquid resin in the tape atop the loop region of coilpossessing a slower rate of reaction to heat than the liquid resinimpregnated into the tape wrapped atop the slot region of the coil.

Although the resin applied to the loop portion of the coil normally willhave no added cure promoter, hard slot, flexible loop coils also can beformed utilizing different concentrations of cure promoter along thecoil to produce a more rapid cure of the insulating resin system appliedto the slot regions of the coil relative to the cure rate of the resinalong the loop regions of the coil. The difference in promoterconcentration between the slot and loop regions of the coil, however,normally is small. For example, the weight ratio of the promoter to theresin in the loop regions generally should be not more than one-halfpercent while a maximum promoter concentration of less than 5 percent byweight of the insulating resin system typically is utilized in the slotregions of the coil.

The single insulating resin system utilized for the coil can varydependent upon the electrical and physical characteristics desired forthe coil. The insulating resin system, however, preferably is athermosetting, nonsolvent containing resin system exhibiting a gel timeat room temperature of at least ten hours, a low volatile content inboth the cured and uncured states and a viscosity suitable forapplication by spraying or brushing. The insulating resin system alsodesirably should be non-toxic and have a cure temperature and timeranging between 24 hours at 100C and 2 hours at 200C.

Because there is some diffusion of the cure promoter at the changeoverlocation in the coil due to the liquid states of the insulating resinsystems applied to the loop and slot regions of the coil, the slowercuring resin system should be applied to the loop region at least 1inch, and normally 2-3 inches, from the end of the slot re gion of thecoil to assure a complete cure throughout the entire slot region. Ifdesired, the insulating resin systems can be color coded with aconventional oil based pigment to facilitate identification of thedifferent resin systems along the coil. Typically, a commerciallyavailable two or three component automatic dispenser is employed toprovide the resin, promoter and pigment in desired quantities and themixture is applied between tape layers by manually brushing theinsulating resin atop tape 14 as the tape is wrapped about coil 10.Because the insulating resin systems applied to the slot and loopregions of the coil are compatible, being formed of the same resiningredients, a single continuous tape can be utilized for wrapping theentire coil. Moreover, because both insulating resin systems are presenton the coil in the liquid state, some diffusion occurs prior to completecuring of the slot regions to inhibit a sharp transition at the junctionof the hard slot to the flexible loop regions of the coil. The entiretransition region, however, must be positioned beyond the slot regionsof the coil to assure a thorough cure of the entire slot regions of thecoil.

Although a differential cure rate in coil 10 preferably is achieved byutilization of differing concentrations of cure promoting catalyst inthe slot regions relative to the loop regions of the coil, flexibleloop, hard slot coils also can be obtained by varying the weightpercentages of epoxy resins having different degrees of functionalityand composition when the insulating resin systems coated between turnsof the tape are formed of a blend of such resins. As is taught inMarkovitz U. S. Pat. application, Ser. No. 216,240, filed Jan. 7, 1972as a Continuation-In-Part of his application 69,481 filed Sept. 3, 1970(now abandoned), the cure rate of an epoxy resin blend can be varied byaltering the weight percentages of dual epoxy resins when the resins aremixed with a cure promoter comprising a titanate and a phenol innon-stoichiometric amounts. For example, a thermosetting resin preparedby mixing parts by weight ERL 4221, 10 parts by weight Epon 828 (abisphenol A-diglycidyl ether epoxy resin having an epoxide equivalentweight between 185 and 192), 1.0 parts by weight bisphenol A and 0.5parts by weight Tyzor 0G (a tetraoctylene glycol titanate containing7.8% Ti) gels in 60 minutes when baked at C while a gel time of 80minutes at 150C is required for equal concentrations of the epoxy resinsutilizing the identical bisphenol A- Tyzor 0G hardener, i.e., athermosetting resin prepared by mixing 50 parts by weight ERL 4221, 50parts by weight Epon 828, 1.0 parts by weight bisphenol A and 0.5 partsby weight Tyzor 00. Because the composition of the insulating resinsystems is substantially identical along the complete length of the coil(except for a variation in the weight percentages of the epoxy resins orthe addition of higher weight percentages of cure promoter in the slotregions of the coil), the insulating resin systems are compatible andcan readily admix in a liquid state along the coil.

After wrapping of the coil with resin impregnated mieaceous tape iscomplete, coil 10 is overwrapped with a release tape 20, such asone-half lap Tedlar (a product of the El. DuPont de Nemours & Company)release tape, and a heat shrinking tape 22, such as onehalf lap Mylar (aproduct of the E.l. DuPont de Nemours & Company) tape. Loop forms andslot guides (the latter being identified by reference numeral 24 in FIG.3), then are placed adjacent the coil and the entire structure issequentially wrapped with layers of release tape and heat shrinking tape26. Because the flexible nature of loop regions .18 in the finished coilpermits adjustment of the clearance between coils during subsequentwinding of the machine, extreme precision is not required in the angleof the coil drop. The entire structure next is heated for a periodrequired to compress the insulation upon the coil, e.g., 150C foronehalf hour to pull down the Mylar heat shrinkage tape,

whereafter the coil is baked, e.g., at 150C for 6 hours, until theinsulating resin system applied to the loop regions is curedsufficiently to accept an application of voltage gradient point normallyutilized as a coating for high voltage insulation. Because of the morerapid cure rate of the slot sections of the coil due to the added curepromoter (or variation in the weight percentage of epoxy resins formingthe insulating resin system) a complete cross-linking of the resinsystem applied to the slot region of the coil preferably also isachieved. The heat shrinking and release tapes, as well as the loopforms and slot guides, then are removed from the coil and the entirecoil is painted with a voltage grading paint having sufficientflexibility to permit raising of previously inserted coil sides duringwinding of the machine. Alternatively, a suitably impregnated asbestosgrading tape could be applied to the coil rather than voltage gradingpaint. Because the loops of the coil are flexible in a cold state due tothe partial cure of the insulating resin system coated therein, there isno need to heat the loops above the glass transition temperature of theinsulation during insertion of the winding into a machine. Thus, inwinding a machine, as is illustrated in FIG. 4, coil sides A and B wouldbe placed in the radially inner coil side positions of slots 28 and 30while the other sides A and B of coils A and B, respectively, would bepositioned in the radially outer coil side positions of slots 32 and 34situated one pole pitch (or a fraction of a pole pitch when a fractionalpitch, e.g., l'ive-sixths pitch, winding is used) away from slots 28 and30. When coil sides C and D are subsequently placed in the outer coilside positions of slots 28 and 30, coil sides A and B must be raised topermit positioning of coil sides C' and D' in the radially inner coilside positions of slots 32 and 34. Raising of the coil sides A and B,however, can readily be accomplished in thecold state because. of theincomplete cure of the insulating resin system on the loop regions ofthe coils. After winding of the machine is complete, the loop regionsare tied into position in conventional fashion to inhibit displacementof the coils during machine operation. If desired, a complete cure ofthe loop regions can be effected after tying the loop regions intoposition to further inhibit displacement of the coils by the electricaland mechanical forces acting thereon.

When superior insulating qualities are desired by virtue of a reducedvoid concentration in the insulation, the coil can be vacuum andpressure processed, prior to application of heat to cause shrinkage ofthe heat shrinking tapes applied to the coil, as illustrated in the flowchart of FIG. 5. Typically, the vacuum/pressure treatment isaccomplished by placing the wrapped coil in a pressure vessel andapplying a vacuum of one-half mm Hb abs for 5 hours, to remove volatileswithin the insulation whereafter the coil is pressurized and heated.Typically, a pressure cycle of 80 psi for 5 hours in a dry gaseousatmosphere with heating to shrink the Mylar tape and cure the resin isemployed. During the higher pressure treatment, the coil temperature israised in excess of I00 C to initially shrink the tapes upon the coilfollowed by-a further raise in temperature to subsequently fully curethe slot regions of the coil in accordance with the proceduresheretofore described relative to FIGS. 1-3.

One coil prepared in accordance with this invention utilized a singlemicaceous tape applied tightly to the coil by hand taping and the lastlayer of tape was adhered by means of the epoxy resin with the resinapplied to the slot regions of the coil containing additionally lpercent by weight tin(ll)octoate. A continuous layer of one mil Tedlarrelease tape, followed by one layer of one-half lap, one mil Mylar heatshrinking tape then was wrapped atop the resin impregnated micaceoustape whereafter slot guides and compression aids were affixed to thecoil by successive layers of Tedlar release tape and Mylar heatshrinking tape, with clamps being employed to insure a tight initialapplication of the slot guards to the slot sections of the coil. Thecoil then was baked at l30C for 6 hours whereafter all the release andcompression tapes were stripped from the coil. The coil exterior nextwas painted with a voltage grading paint and the coil was baked at 127Cfor 2 hours to harden the paint. An air drying alkyd varnish then wasspray coated atop the coil to improve the appearance of the coilsurface. The finished coil exhibited good flexibility in the loopsections and good rigidity in the slot section.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A method of winding a dynamoelectric machine comprising shaping atleast one conductor into a closed loop coil having elongated slotregions for insertion within a magnetic member of a dynamoelectricmachine and loop regions interconnecting the ends of the slot regions,wrapping said coil with a single tape coated with a thermosettinginsulating system having differential cure rates between the slot andloop regions of the coil, curing said thermosetting insulating systemfor a period sufficient to impart rigidity to the insulation system inthe slot region of the coil while only partially curing the insulationgsystem on the loop regions of said coil thereby to maintain flexibilityin the insulation system on the loop regions of said coil, and insertingthe rigid slot portions of the coil through axial slots in amagnetizable member of a dynamoelectric machine thereby to position theflexible loop regions of the coil outward from the ends of said axialslots, to form a machine winding, the flexibility of said loop regionsbeing effective to facilitate raising one of the slot regions of saidcoil with respect to the other slot region thereof to permit subsequentinsertion of other coil sides under said one slot region of the coil.

2. A method of winding a dynamoelectric machine according to claim 1wherein said differential cure rate is achieved by coating the tape witha single insulating resin system containing differential quantities of across-linking promoter in the slot regions relative to the loop regionsof the coil.

3. A method of winding a dynamoelectric machine according to claim 2wherein said resin system applied to the loop regions of the coilcontains no cure prometer.

4. A method of winding a dynamoelectrie machine according to claim Iwherein a differential cure rate is achieved by coating the tape with ablend of epoxy resins having different degrees of functionality andcomposition, the relative percentages of said resins in said slotregions differing from the relative percentage of said resins in saidloop regions of said coil.

5. A method of winding a dynamoelectric machine according to claim 1further including wrapping said coil with a release tape subsequent towrapping the coil with the resin coated tape, applying vacuum to saiddual wrapped coil to remove volatiles, pressurizing the coil with agaseous atmosphere and subsequently curing the insulation system on thecoil for the period required to produce a hard slot, flexible loop coil.

I. I I I

2. A method of winding a dynamoelectric machine according to claim 1wherein said differential cure rate is achieved by coating the tape witha single insulating resin system containing differential quantities of across-linking promoter in the slot regions relative to the loop regionsof the coil.
 3. A method of winding a dynamoelectric machine accordingto claim 2 wherein said resin system applied to the loop regions of thecoil contains no cure promoter.
 4. A method of winding a dynamoelectricmachine according to claim 1 wherein a differential cure rate isachieved by coating the tape with a blend of epoxy resins havingdifferent degrees of functionality and composition, the relativepercentages of said resins in said slot regions differing from therelative percentage of said resins in said loop regions of said coil. 5.A method of winding a dynamoelectric machine according to claim 1further including wrapping said coil with a release tape subsequent towrapping the coil with the resin coated tape, applying vacuum to saiddual wrapped coil to remove volatiles, pressurizing the coil with agaseous atmosphere and subsequently curing the insulation system on thecoil for the period required to produce a hard slot, flexible loop coil.